1. Field
Embodiments of the invention relate to the field of networking; and more specifically, to optical networks.
2. Background
Generalized Multiprotocol Label Switching (GMPLS) [RFC3471] extends the Multiprotocol Label Switching (MPLS) architecture [RFC3031] to encompass time-division (e.g., Synchronous Optical Network and Synchronous Digital Hierarchy, SONET/SDH), wavelength (optical lambdas) and spatial switching (e.g., incoming port or fiber to outgoing port or fiber).
GMPLS extends MPLS to include network devices whose forwarding plane recognizes neither packet, nor cell boundaries, and therefore, can't forward data based on the information carried in either packet or cell headers. Specifically, such network devices include devices where the forwarding decision is based on time slots (TDM), wavelengths (lambda), or physical (fiber) ports. GMPLS supports uni-directional label switched paths (LSPs) and bi-directional LSPs (For bi-directional LSPs, the term “initiator” is used to refer to a node that starts the establishment of an LSP and the term “terminator” is used to refer to the node that is the target of the LSP; Note that for bi-directional LSPs, there is only one “initiator” and one “terminator”) and a special case of Lambda switching, called Waveband switching (A waveband represents a set of contiguous wavelengths which can be switched together to a new waveband; The Waveband Label is defined to support this special case; Waveband switching naturally introduces another level of label hierarchy; As far as the MPLS protocols are concerned there is little difference between a waveband label and a wavelength label.).
To deal with the widening scope of MPLS into the optical and time domain, there are several new forms of “label.” These new forms of label are collectively referred to as a “generalized label.” A generalized label contains enough information to allow the receiving node to program its cross connect, regardless of the type of this cross connect, such that the ingress segments of the path are properly joined. The Generalized Label extends the traditional label by allowing the representation of not only labels which travel in-band with associated data packets, but also labels which identify time-slots, wavelengths, or space division multiplexed positions. For example, the Generalized Label may carry a label that represents (a) a single fiber in a bundle, (b) a single waveband within fiber, (c) a single wavelength within a waveband (or fiber), or (d) a set of time-slots within a wavelength (or fiber). It may also carry a label that represents a generic MPLS label, a Frame Relay label, or an ATM label (VCI/VPI).
Thus, GMPLS forms label switched paths (LSPs) through the network. These paths may be connection oriented or connectionless. For instance, the Resource Reservation Protocol (RSVP) is often used to deploy connection oriented LSPs, whereas a label management protocol (LMP), such as the label distribution protocol (LDP), is often used to provision connectionless LSPs.
Optical Networks
An optical network is a collection of optical network devices interconnected by links made up of optical fibers. Thus, an optical network is a network in which the physical layer technology is fiber-optic cable. Cable trunks are interconnected with optical cross-connects (OXCs), and signals are added and dropped at optical add/drop multiplexers (OADMs). The optical network devices that allow traffic to enter and/or exit the optical network are referred to as access nodes; in contrast, any optical network devices that do not are referred to as pass-thru nodes (an optical network need not have any pass-thru nodes). Each optical link interconnects two optical network devices and typically includes an optical fiber to carry traffic in both directions. There may be multiple optical links between two optical network devices.
A given fiber can carry multiple communication channels simultaneously through a technique called wavelength division multiplexing (WDM), which is a form of frequency division multiplexing (I-DM). When implementing WDM, each of multiple carrier wavelengths (or, equivalently, frequencies or colors) is used to provide a communication channel. Thus, a single fiber looks like multiple virtual fibers, with each virtual fiber carrying a different data stream. Each of these data streams may be a single data stream, or may be a time division multiplex (TDM) data stream. Each of the wavelengths used for these channels is often referred to as a lamda.
A lightpath is a one-way path in an optical network for which the lamda does not change. For a given lightpath, the optical nodes at which its path begins and ends are respectively called the source node and the destination node; the nodes (if any) on the lightpath in-between the source and destination nodes are called intermediate nodes. An optical circuit is a bi-directional, end to end (between the access nodes providing the ingress to and egress from the optical network for the traffic carried by that optical circuit) path through the optical network. Each of the two directions of an optical circuit is made up of one or more lightpaths. Specifically, when a given direction of the end to end path of an optical circuit will use a single wavelength, then a single end to end lightpath is provisioned for that direction (the source and destination nodes of that lightpath are access nodes of the optical network and are the same as the ends nodes of the optical circuit). However, in the case where a single wavelength for a given direction will not be used, wavelength conversion is necessary and two or more lightpaths are provisioned for that direction of the end to end path of the optical circuit. Thus, a lightpath comprises a lamda and a path (the set of optical nodes through which traffic is carried with that lambda).
Put another way, when using GMPLS on an optical network, the optical network can be thought of as circuit switched, where LSPs are the circuits. Each of these LSPs (uni-directional or bi-directional) forms an end to end path where the generalized label(s) are the wavelength(s) of the lightpath(s) used. When wavelength conversion is not used for a given bi-directional LSP, there will be a single end to end lightpath in each direction (and thus, a single wavelength; and thus, a single generalized label).
An optical network device can be thought of comprising 2 planes: a data plane and a control plane. The data plane includes those components through which the light travels (e.g., the switch fabric or optical crossconnect; the input and output ports; amplifiers; buffers; wavelength splitters or optical line terminals; adjustable amplifiers; etc.), add/drop components (e.g., transponder banks or optical add/drop multiplexers, etc.), and components that monitor the light. The control plane includes those components that control the components of the data plane. For instance, the control plane is often made up software executing on a set of one or more microprocessors inside the optical network device which control the components of the data plane. To provide a specific example, the software executing on the microprocessor(s) may determine that a change in the switch fabric is necessary, and then instruct the data plane to cause that switch to occur. It should also be noted that the control plane of an optical network device is in communication with a centralized network management server and/or the control planes of one or more other network devices.
A number of different network topologies have been developed for optical network devices, including ring and meshed based topologies. Similarly, a number of different control planes and data planes have been developed for optical network devices. For instance, wavelength division multiplexing (WDM) necessitated an alteration of the data plane and the control plane. As another example, various different techniques have been used for implementing the switch fabric, including optical cross connects such as MEMS, acousto optics, thermo optics, holographic, and optical phased array.
Operating an optical network typically requires: A) building and maintaining network databases; and B) establishing lightpaths. For example, the network databases can include: 1) link state databases that track information (e.g., the link(s), lamda(s), lamda bandwidths, etc.) regarding adjacent optical nodes (e.g., using a link management protocol (LMP)); and 2) topology databases that track information (e.g., nodes, links, lamdas, etc.) for the physical connectivity of the nodes in a domain and/or the entire network (e.g., using OSPF-TE). In order to establish an LSP, the following operations are typically performed offline: 1) determining a shortest path/wavelength between the source and destination using a shortest path first algorithm based on the network database(s); 2) allocate that path/wavelength (often referred to as signaling the path; effectively telling the involved optical network devices how to configure their switch fabrics; e.g., using RSVP or CR-LDP based signaling with GMPLS). Steps 1 and 2 can be reversed.
There are generally three approaches to operating an optical network: 1) centralized static provisioning; 2) source based static provisioning; and 3) hybrid static provisioning. In centralized static provisioning, a separate centralized network management server maintains a network topology database and communicates with each of the optical network devices of a network. In response to some predefined demands for an optical circuit, the network management server finds the shortest path/wavelength. The network management server then causes the allocation of the path/wavelength and the configuring of the switch fabrics.
In source based static provisioning, each of the access nodes of the network performs the work of building/maintaining a network topology database. In response to some predefined demands for an optical circuit received by an access node, that node: 1) buffers the traffic as necessary; 2) finds the shortest path/wavelength; and 3) causes the allocation of the path/wavelength and the configuring of the switch fabrics.
In hybrid static provisioning, each of the nodes of the network use OSPF-TE to build network topology databases, and from there a network topology database is built and maintained in a centralized network management server. The network management server initiates a form of source based provisioning. This allows a network administrator to maintain control over provisioning of each lightpath provisioned.
One problem with existing optical networks is the network topology databases used and the manner in which they are built and maintained. Specifically, these monolithic physical topology databases (e.g., built with OSPF-TE) are very large because they must store all of the data to give a physical view of the network (not only connectivity at the link level, but connectivity at the lamda level because there are multiple lamdas per link and because different lamdas on a given link may provide different bandwidths; etc.). These large network databases are relatively time consuming to parse and require a relatively long time and a relatively large amount of node intercommunication to propagate changes. In addition, such network topology databases would become even larger if QoS type information needed to be recorded.
Another problem with existing optical network devices is there static, off-line nature of operation (e.g., using centralized static provisioning, source based static provisioning, hybrid static provisioning, etc.). More particularly, based upon a determination of the projected needs of the end node to end node connection through the optical network and the then existing state of the optical network (basically, a snapshot of the network parameters), an optical circuit is provisioned through the optical network over which the traffic is to travel. This optical circuit will be static in the sense that it will not be altered on the fly based upon current bandwidth requirements (demand changes), current status of the network, etc. Instead, this optical circuit will only be modified when it is re-provisioned (e.g., at the request of the customer to upgrade to a larger or smaller amount of bandwidth) and/or some form of protection switch based on a redundancy scheme.
Therefore, a given optical circuit is established at the maximum bandwidth believed to be required at any given point in time, and this maximum bandwidth is provisioned for that purpose. That is to say, a given customer is provisioned a fixed amount of bandwidth for all classes of traffic, whether that customer at any given point in time is using some, all or none of that bandwidth. Due to variations in the bandwidth requirements and/or the status of the network, bandwidth will go unused.
Thus, the optical layer is operated to provide point-to-point links, with no intelligence and no real time decision-making capabilities. In addition, the need for demands to be known in advance imposes difficulties for service creation and service provisioning. This results in an inefficient utilization of resources at the optical layer.
Furthermore, while there has been work to provide quality of service (QoS) at the IP layer and/or using MPLS, both of these protocols are carried over SONET; where SONET does not distinguish the types of traffic (does not provide QoS). Thus, typical optical control planes do no provide the ability to separate traffic into different classes based on service level requirements (i.e., they do not incorporate service level requirements of different types of traffic in lightpath calculations).